Cumene hydroperoxide (hereinafter “CHP”) is commonly produced using one or more well known methods of oxidation of cumene with air oxygen at a high temperature, i.e., oxidation takes place in liquid-gas system. Typically, cumene is oxidized until CHP concentration reaches 20-35 wt. %, because further increase in cumene conversion leads to a significant build-up of by-products resulting in a proportionally lower process selectivity. The oxidation products are then delivered to a vacuum stripping stage where unreacted cumene is distilled. The stripping bottom product containing about 60-93 weight percent of CHP is then delivered to a CHP cleavage stage, where CHP decomposes into acetone and phenol under influence of an acidic catalyst. It is well known that in conventional oxidation processes, the main CHP formation reaction is accompanied by a number of side reactions.
The effect of side reactions on the main CHP formation reaction depends, among other factors, on process conditions such as one or more of the following: temperature, product residence time in the reactors, and cumene conversion degree. Typically, the main by-products formed in the side reactions are dimethylbenzene alcohol (hereinafter ‘DMBA’), acetophenone (hereinafter “AP”) to and organic acids, such as formic acid, acetic acid, and/or benzoic acid. Formic and benzoic acids serve to catalyze the acidic decomposition of CHP to form phenol and acetone.
The presence of phenol in the reaction products, under the conditions of a radical oxidation process, is extremely undesirable because it results in a dramatic inhibition of the CHP formation reaction and has a significant negative impact on the overall process selectivity. In fact, research has demonstrated that when employing conventional previously known process technologies, (i.e. without special treatment of the cumene oxidation products with ammonia), the rate of oxidation of low-quality cumene (in which sulfur-containing trace contaminants are present) is so slow that such conventional technologies could scarcely be considered acceptable for commercial processes. Moreover, when the CHP concentration reaches about 20 wt. %, the conversion of cumene starts to decrease, which leads to complete termination of the reaction. The undesirably low rate of reaction at the initial period is a result of the presence of inhibitors that are contained in the cumene, (most commonly, sulfur-containing contaminants). Specifically, the reason for the inevitable slow-down of the oxidation rate over a course of time, is the joint influence on the reaction of inhibitors accumulated in the reactor due to the oxidation reaction itself, as well as inhibitors introduced with fresh cumene. In fact, the rate of formation of radicals in the reactor turns out to be slower than the rate of the radical chain propagation, which leads to the suppression of the process.
There are several ways to avoid the formation of phenol as oxidation inhibitor. Most of them are well known in the art and involve the use of alkali agents such as hydroxides of alkaline metals and their carbonates as well as high molecular carbon salts at cumene oxidation. Such methods are described in greater detail in the U.S. Pat. No. 3,187,055 issued Jun. 1, 1965, and in the U.S. Pat. No. 2,796,439 issued Jun. 18, 1957.
A general disadvantage of previously known methods (for example, such as described in the above-identified patents) is the need for careful separation of added reagents from the oxidation products formed during the reaction, which is a difficult practical engineering problem. This separation is essential because the presence of added reagents has an adverse impact on further stage of CHP concentration by increasing the expressiveness of the process and initiating partial decomposition of CHP into byproducts such as DMBA and Acetophenone. The overall CHP losses to the byproducts can be about 1-1.5% (absolute), which is impermissible and undesirable in most large-scale process. Furthermore, the presence of alkali compounds, not only dramatically complicates the stage of acidic CHP decomposition into phenol and acetone, but also exposes this stage to significant potential dangers.
Other methods of cumene oxidation—for example in the presence of aqueous solutions of alkaline agents—are also known in the art and are disclosed in U.S. Pat. No. 2,663,740, issued Mar. 5, 1952, USSR Author's certificate No. 567723, filed May 16, 1975, and in USSR Author's certificate No. 858313, filed Aug. 21, 1981. The above-mentioned alkaline agents and carbonates of alkaline agents as well as ammonia and tetralkylammonia base solutions are related to the aqueous solutions of alkaline agents. Thus, these to methods of the oxidation process conduction are not free of the above-described disadvantages.
There are also known methods of continuous cumene oxidation to CHP in without use of catalysts, initiators, and alkaline agent additives where the mixture of initial and recycle cumene streams is treated from impurities inhibiting the oxidation process by washing the mixture with aqueous sodium hydroxide and water solution. One such method is disclosed in U.S. Pat. No. 3,907,901; issued on Sep. 23, 1975. However, the disadvantages of this, and similar methods are:
1) A low feed oxidation rate (e.g., 1.5-2 weight % t per hour) that requires an increase in the reaction volume of the reactors to provide the required unit productivity (this also results in higher process costs); and
2) Low process selectivity with regard to desired product (91-92 mole %).
The Russian patent No. 2146670, published on Mar. 20, 2000, proposes a solution by which the problem of selectivity, and therefore minimization of losses at CHP concentration stage, is resolved by the division of the process into two steps. At the first step, the process is carried out with pure cumene, freed from alkaline agents. A base, such as NH4OH, is added into a first reactor of a series of sequential reactors and supplied with water. Cumene oxidation products coming out from a last series reactor are forwarded to a CHP concentration stage, and recycle cumene streams from the CHP concentration stage, an off-gas condensation stage, and an alpha-methylstyrene (hereinafter “AMS”) hydrogenation stage, are treated with NaOH, (NH4NaCO3+NH4OH), NH4OH and H2O in a technologically complicated scheme.
Although a sufficiently high selectivity was achieved by implementing this process without discharging of the process inhibitor (specifically, phenol), and injection of water into the reactor, the rate of CHP formation in the reactors is relatively low, i.e. 2.8 wt. % to 3.0 wt. % per hour. This approach requires the use of very large reactor volumes, and therefore results in significantly higher capital investment in implementing the process. In cases of revamps of existing plants, high volume reactors may make this process impossible to implement due to space considerations.
Other inhibitors of CHP formation reaction (such as sulfur-containing trace contaminants, etc.) that may be present as a result of utilization of lower-grade cumene, also have a considerable negative effect on the process. In fact, research has demonstrated that when employing most conventional previously known process technologies, (i.e., without special treatment of the cumene oxidation products with ammonia), the rate of oxidation of low-quality cumene (in which sulfur-containing trace contaminants are present) is so slow that such conventional technologies could scarcely be considered acceptable for commercial processes.
Moreover, when the CHP concentration reaches about 20 wt. %, the conversion of cumene starts to decrease, which leads to complete termination of the reaction. The undesirably low rate of reaction at the initial period is a result of the presence of inhibitors that are contained in the cumene, (most commonly, sulfur-containing contaminants). Specifically, the reason for the inevitable slow-down of the oxidation rate over a course of time, is the joint influence on the reaction of inhibitors accumulated in the reactor due to the oxidation reaction itself, as well as inhibitors introduced with fresh cumene. In fact, the rate of formation of radicals in the reactor turns out to be slower than the rate of the radical chain propagation, which leads to the undesirable suppression of the process.
It would thus be desirable to provide a process for production of CHP that is capable of producing CHP at a higher process selectivity, with greater safety, and lower expense than previously known techniques. It would also be desirable to provide a process for production of CHP that is capable of utilizing lower-grade cumene comprising oxidation process inhibiting trace elements (e.g., sulfur-containing trace compounds, etc.), while producing CHP at a substantially the same or higher process selectivity than any of the previously known processes utilizing a higher grade of cumene in CHP production. It would moreover be desirable to provide a process for producing CHP, that decreases the amount of preexisting and by-product process inhibitors during the cumene oxidation reaction, thereby raising the process selectivity and improving process safety.